Process for the production of naphthalene



United States Patent Kentucky Filed Oct. 5, 1959, Ser. No. 844,366

17 Claims. (Cl. 260--672) This invention rel-ates to a process for producing naphthalene and is particularly concerned with a process by which a high yield of naphthalene may be obtained from various hydrocarbon fractions containing polycyclic aromatics.

The commercial importance of naphthalene resides to a large extent in its use as an intermediate in the production of phthalic anhydride, one molecule of naphthalene being oxidized to produce one molecule of phthalic acid, which is in turn dehydrated. In a recent year, for example, roughly 80% of all the naphthalene domestically produced was consumed in the production of phthalic anhydride.

Heretofore the only commmercial source of naphthalene hasbeen coal tar, from which it is produced as a byproduct of the destructive distillation of coal in the manufacture of coke. Since the commercial production of coke is tied directly to the refining of iron ore, the production of naphthalene from this source has long vacillated with the fortunes of the steel industry. Recently, however, the chemical industry has required greater quantities of naphthalene than are presently produced from coal tars, and at the same time a constant supply not subject to such wide fluctuations was desired. This invention, therefore, is directed to a process whereby naphthalene may be produced from any hydrocarbon fraction containing polycyclic aromatics to meet this economic need. A specific example is included showing how naphthalene may be produced from petroleum.

Naphthalene is not present to any significant extent in crude petroleum. While the amount varies with the source of the crude, the total of all aromatic hydrocarbons in crude petroleum is only about 5%. Separation by fractionation of such naphthalene as is present has not proven feasible because of the large number of other compounds having boiling points close to its own. (Pure naphthalene boils at 424 -F.) However, certain fractions of petroleum products from processes such as catalytic reforming, catalytic cracking and thermal cracking docontain significant quantities of naphthalene and alkylsubstituted naphthalenes. This invention is a process whereby such alkylnaphthalenes are hydrodealkylated to produce an excellent yield of high purity naphthalene. The cost and purity of the naphthalene so produced .are at least comparable to those of naphthalene produced by other processes, such as those presently employed in the coal tar industry. Furthermore, practice of this invention terminates the dependence of naphthalene consumers on the coke and steel industries by providing a constant alternative source of supply.

The present process is capable of effectively dealkylating the alkyl-substituted naphthalenes present in a given hydrocarbon fraction. The greatest significance of the process from a commercial standpoint, consequently, lies particularly in the dealkylation of a hydrocarbon fraction which is relatively rich in alkylnaphthalenes, or, more generally, which is relatively rich in polycyclic aromatics since alkylnaphthalenes are typically present with other polycyclic aromatics. Thus, it will be understood that a polycyclic-rich fraction comprises a preferred feed stock on which the invention is adapted to be practiced, al-

. preferably employed in the 3,075,022 Patented Jan. 22, 1963 "ice though it is not the only stock on which the process will operate effectively.

Hydrocarbon fractions rich in polycyclic aromatics frequently contain as major impurities sulfur compounds such as thiophenes and higher boiling sulfur ring compounds such as thionaphthalene. These compounds display boiling points close to that of naphthalene and therefore cannot be removed by a fractionation procedure. Coal tar producers, in order to meet the increasingly high purity standards required of naphthalene, remove thiophenes by a relatively expensive acid treatment. The present invention removes such impurities as an incident to the hydroidealkylation of the feed stock in which they are present. Consequently, a relatively pure product is obtained without the need of separate purification operations.

Typical reformate stocks produced in the catalytic reforming of hydrocarbons are relatively rich in alkylnaphthalenes. We have found that a high yield of relatively pure naphthalene can be obtained from such feed stocks by subjecting the stock to hydrodealkylation at temperatures above 1200 F. in the presence of aspecialized chromia catalyst.

More specifically, we have found that a catalyst consisting of approximately 10-15% by weight of chromium oxide on a high purity, low sodium content, gamma type alumina support is capable, in the presence of hydrogen, of dealkylating substituted naphthalenes present in heavy 'reformate or the like and concurrently removing sulfurbearing impurities, at temperatures above l200 F. Otherwise put, we have discovered that a catalyst of the type specified and under the conditions indicated will selectively split off alkyl groups attached to naphthalene rings without cracking naphthalene to alkylbenzenes or benzene, so that conversions in excess of of the available alkyln aphthalene compounds to naphthalene are obtained with negligible coke formation.

One catalyst which enables suchresults to be obtained, in contrast to the poor results obtained in the use of conventional chromia and other catalysts on conventional supports, is commercially available from The Girdler Construction Division, PO. Box 174, Louisville 1, Kentucky, under their trade designation G-41. X-ray defractio-n patterns show the chromia :oxide to be present in the form of hexagonal crystals, as distinguished from chromia aluminum co-gel catalysts which have also been available 'but which are incapable of providing similar results. The total chromia content of 'the commercial product is calculated at 11.8% C 'byweight, the remainder of the product being the specified high purity, low sodium content, gamma type alumina. The catalyst is form of tablets, for example, x A in size, forming a fixed bed through which the feed stock and hydrogen are passed continuously. However, other tablet sizes may be used, in single or multiple fixed bed reactor systems or moving bed reactor systems. Likewise, pulverized catalyst may be employed in a fluidized type reactor. The only limitation on reactor design is the satisfactory contacting of feed with catalyst at the prescribed space rates. The catalyst effectively dealkylates in a single pass operation, so that recirculation of the unconverted product is not required. However, under certain conditions, the recycling of naphthalene bottoms product may lead to higher yields. Under normal conditions coke yields are so low as not to show up in an ordinary material balance. Furthermore, the catalyst may be periodically regenerated by burning off coke deposits, as is more fully described below. 7

The process of this invention is effected by contacting the polycyclic rich aromatic charge with the catalyst and hydrogen at a temperature above 1200" F2, and preferably at. a temperature of approximately 1350 F., at a weight hourly space velocity preferably between about I 0.5 and 2.0. Since dealkylation of alkyl aromatics and polycyclics present in the charge stock is accompanied by heat liberation, the feed may be held at a temperature somewhat lower than the preferred 1350 F. temperature. The molar ratioof hydrogen to hydrocarbon feed stock is not critical and may be, for example, approxirnately 7:1. For economic operation, the ratio should be adjusted to give minimum coking, in accordance with Well-known techniques. I

Within the contact zone dealkylation occurs rapidly, but even at the high temperature indicated there is little destructive cracking of hydrocarbons into coke or normally gaseous products and little formation of undesirable alkylbenzenes or saturated products. In the cracking zone, alkyl-groups split ofi the alkylnaphthalenes to yield naphthalene, whilethe sulfur impurities are converted into hydrogen sulfide and the paraflin impurities are cracked to gas. The normally liquid products from the hydrocracker are then condensed, and the gaseous products are separated from the liquid products by means of a flash drum and absorber. Dry gas products may be used for plant fuel, while the'liquid products are stabilized to remove entrained or absorbed gas, and the liquid products are then subjected to fractionation, crystallization or other means of separation to separate naphthalene from the other components.

Thegeneral type of reaction carried out in the present process is as follows:

catalyst where R is an alkyl radical.

A preferred feed stock upon which the process may be practiced comprises a 400-600 F. catalytic reformate or an aromatic extract from a 400-600 F. hydrocarbon fraction. Such an extract may be obtained from a hydrocarbon fraction containing polycyclic aromatics by a number of known solvent extraction and solid bed adsorption processes such as the well-known Udex process, in which the aromatics are selectively extracted from the reformate by a mixture of 'diethylene glycol and water.

The product of hydrodealkylating such a feed stock in accordance with this invention is comprised as follows, typical ranges being given:

' Percent by weight Benzene 18 Toluene 0-10 Xylenes 0-5 Naphthalene 33-58 The conversion of alkylnaphthalenes present in the feed stock to naphthalene is excellent; tests indicate conversions as high as 90%. In general, the purity and yield of the naphthalene fractionated from the product increase with increasing reactor temperature (up to that point at which the naphthalene itself begins to be cracked) as the result of the fact that the impurities in its boiling range are more completely cracked at higher reactor temperatures. Sulfur compound impurities such as thiophene, tmonaphthene and thionaphthalene present in the charge are broken up into H 8 and saturated hydrocarbons; paraflins are also cracked with increasing temperature. However, if the temperature is increased beyond the temperature at which the alkylnaphthalenes are dealkylated, the condensed ring compounds then themselves split into alkylbenzenes, which are finally converted to benzene, because the optimum temperature has been exceeded. Saturation ofjring compounds does not occur to any significant extent because at the temperatures involved, the equilibrium points he far toward the side of unsaturation. One method'of practicing the invention continuous on a commercial scale as an adjunct to a petroleum refining a space velocity,

operation at which a feed stock of the type specified is available is illustrated in the accompanying diagram. The hydrogen employed for the dealkylation is taken from a refinery off-gas the light hydro-carbon components of which play no part in the reaction and have no eifect on theprocess. V

The feed stock is fed through line 1 to feed pump 2, from which it goes to an absorber 3. In the absorber, vapors from a flash drum are passed through the feed streain whereby valuable liquid product contained in the vapor is recovered, while thedry gas from the absorber is drawn on through line 4 for use as plant fuel. The function of the absorber is merely one of recovery and serves to reclaim any valuable product remaining in the flash drum oif gas. Its use is not imperative to the suc cessful practice of the invention. Likewise, it is not necessary that thefeed stock be used as the adsorbent oil to recover product from the flash drug gas; Any ab= sorbent from which the product can be subsequently sepa rated may be used.

Hydrogen supplied by a hydrogen rich reformer olfgas passes through line 5 to a gas compressor 6, from which it flows in line 7.

Feed stock moving in line 8 from the absorber 3 is mixed inline 9 with the hydrogen coming from the gas' compressor 6. This mixture is fed into a heater 10. The heater raises the temperature of the hydrogen-feed stock mixture to a level at which hydrodealkylation of the feed stock is effected. As noted, this temperature is above 1200 F. and is preferably about 1350 F. Since the tiealkylation reaction is itself exothermic, the feed may be heated prior to its introduction into the reactor to a temperature somewhat less than the preferred 1350 F. temperature at which conversion is effected. For exam ple, where the dealkylation is to be conducted at a term perature within the reactor of 1350 F. the feed tent perature may be approximately 1250 F. The feed tem= perature thus provides a convenient means of adjusting the temperature in the reaction zone. Alternatively, the re-' actor may be surrounded with a heat exchanger to' carry 01f the heat generated by the reaction. Reactor temperature also will vary of course, with the weight hourly space velocity of the feed stock in the reactor.

From the heater, the hot gas flows through line 11 to reactor 12 into which it is introduced at the top, passing downwardly over a fixed bed of catalyst, as is described subsequently. A pressure of approximately 500 p.s.i.g. is maintained in the reactor. The reactor pressure may be varied from approximately to 1000 p.s.i.g., the intermediate pressure described herein being an operating pressure which it is practical to employ.

The reactor is not of a critical design. It may, for example, be of the tubular, fixed or moving bed, or chamber reactor type. Alternatively, as noted, it may be of the type wherein the catalyst is fluidized. It is thus sufficient merely to dispose the-catalyst so that it may contact the feed stock and hydroge The weight hourly that is, the number of pounds of feed stock-introduced per hour into the reactor per pound of catalyst, is preferably about 0.9 pound; typical reaction time is of the order 3-6 seconds, although neither of these figures is in any sense critical.

The partial pressure of hydrogen in the reactor should be adjusted, in accordance with well known procedures, to produce minimum coking in the reactor. Suflicient hydrogen must, of course, be added to effect dealkylation, saturate the alkyl groups removed from the double rings, and minimize subsequent cracking.

Under the conditions indicated, catalyst life is good. Coke deposits in quantities suflicient to deactivate the catalyst are not formed on the catalyst until more than two barrels of feed stock per pound of catalyst have been processed. When the'catalyst does become inactive due to coke deposits, it can be regenerated by burning off the coke deposits with air at high temperature.

The reactor output passes through line 23 to a condenser 14 wherein the liquid product is condensed. The output stream then passes through line 15 to a flash drum 16 wherein remaining gases are liberated from the liquid stream and are returned by line 17 to the absorber'3, where they are dried by contact with the incoming feed stock.

Liquid product from the flash drum is passed through line 18 to stabilizer 1 9 Where the volatile light hydrocarbon gases are removed. This residual light gas is drawn off from the stabilizer through line 20 to be used as plant fuel. The bottom product coming from the stabilizer through line 21 comprises a mixture of benzene, toluene, xylenes, naphthalene and high boiling compounds as has been described previously. These may be separated by subsequent fractionation.

A typical material balance of the process is as follows:

Temperature F 1392 Pressure p.s.i.g 510 WHSV 0.93 H/hydrocarbon ratio 8.44/ 1.0

Product Analysis Benzene percent by Weight 18 Toluene do 3 Xylenes Trace Naphthalene percent by Weight 57.7 Naphthalene Cut do 55.8 Freeze point (C.) do 79.91 Purity (mol percent) do 99.3

I This is the fraction cut out of the full range product.

While the product of this invention is of high purity, it occasionally happens that its acid Washed color does not meet the color standard which is required of refined grade naphthalene. Such discoloration is believed to be due to the presence of trace quantities of indene or indan compounds. We have discovered that this discoloration, when it occurs, may readily be removed to produce a product meeting the prescribed standard, by treatment with hot clay at about 500 F. Specifically, the naphthalene is contacted with clay at about this temperature, whereby the undesirable impurities are removed. It is desirable, although not necessary, to employ this hot clay treatment subsequent to the firactionation of the dealkylation eflluent in order that the bulk of any indene present in the efiluent is not lost but may be recovered from the tractionator.

Having described our invention, we claim:

1. The process of producing naphthalene from a hydrocarbon ieed stock containing alkylnaphthalene compounds which process comprises subjecting the feed stock to hydrodealkylating conditions in the presence of hydrogen and a catalyst consisting of approximately 10 to 15% by weight of chromia on a high purity low sodium content gamma type alumina support at .a temperature above approximately 1200 F.

2. The process of claim 1 wherein the temperature is approximately 1350 F.

3. The process of claim 1 wherein the hydrogen is supplied in the form of a hydrogen-rich ofi gas obtained from a catalytic reformer.

4. The process of claim 1 wherein the hydrocarbon feed stock boils in the range from 400-600" F. and is selected from the class consisting of heavy petroleum reformate, thermally cracked light cycle oil, and catalytically cracked light cycle oil.

5. The process of claim 1 wherein the hydrocarbon feed stock is an aromatic extract of a hydrocarbon boiling in the range from 400600 F.

6. The process of claim '1 wherein the hydrodealkylated product is separated into a lighter traction and a residual bottoms fraction and the bottoms fraction is recycled to the reaction zone.

'7. The process of claim 1 wherein the catalyst consists of approximately -11.8% chromia on the said support.

8. Theprocess of claim l wherein the chromia is in the form of hexagonal crystals.

9. The process of claim 1 wherein the hydrodealkylation is conducted by passing a stream of the feed stock through a'fixed bed of said catalyst.

10. The process of producing naphthalene from a feed stock relatively-rich in polycyclic aromatic compounds which process comprises subjecting the feed stock to hydrodealkylating conditions in the presence ofhydrogen and a catalyst consisting of approximately 10 to 15% by weight of chromia on a high purity low sodium content gamma type alumina support at a temperature above approximately 1200 F. whereby alkyln-aphthalene compounds present in said feed stock are selectively dealkylated to produce naphthalene.

11. The process of producing naphthalene which process comprises subjecting a feed stock containing alkylnaphthalene compounds to a catalyst consisting of approximately 10 to 15 by weight of chromia on a high purity low sodium content gamma type alumina support at a temperature above approximately 1200 F. in the presence of hydrogen.

12. The process of producing sulfur-free naphthalene which process comprises subjecting a feed stock contain ing alkylnaphthalene compounds to a catalyst consisting of approximately 10 to 15% by weight of chromium oxide on a high purity low sodium content gamma type alumina support at a temperature above approximately 1200 F. in the presence of hydrogen for a period of time sufficient to convert the alkylnaphthalene compounds into naphthalene and gas, and separating the gas from the naphthalene so produced.

13. The process of producing sulfur-free naphthalene from a feed stock relatively rich in polycyclic aromatic compounds which process comprises subjecting the feed stock to hydrodealkylating conditions in the presence of hydrogen and a catalyst consisting of approximately 10 to 15% by weight of chromia on a high purity low sodium content gamma type alumina support at a temperature above approximately 1200 F. whereby alkylnaphthalene compounds present in said feed stock are dealkylated to produce naphthalene without commensurate production of benzene and al-kylbenzene compounds.

14. The process of producing naphthalene from a hydrocarbon feed stock containing alkylnaphthalenes and sulfur compound impurities which process comprises, subjecting the feed stock to a catalyst comprising approximately 10 to 15% by weight of chromium oxide on a high purity, low sodium content gamma type alumina support, at a temperature in the range from approximately 1200" F. to 1400 F., at a pressure in the range from to 1000 p.s.i.g., at a weight hourly space velocity in the range from 0.5 and 2.0, whereby the alkylnaphthalene compounds are converted to naphthalene and gas, and whereby said sulfur compound impurities are removed.

15. The process of producing refined grade naphthalene from a hydrocarbon feed stock containing alkylnaphthalenes which process comprises, subjecting the feed stock to a catalyst comprising approximately 10 to 15% by weight of chromium oxide on a high purity, low sodium content gamma type alumina support, at a temperature in the range from approximately 1200 F. to 1400 F., at a pressure in the range from 100 to 1000 p.s.i., at a weight hourly space velocity in the range from 0.5 and 2.0, whereby the :alkylnaphthalene compounds are converted to naphthalene and gas, fractionating the naphthalene from the dealkylation effluent, and contacting the fractionated naphthalene with hot clay at about 500 F.

16. In the process of producing naphthalene from a hydrocarbon containing .alkylnaphthalenes which process comprises, subjecting the feed stock to a catalyst comprising approximatelyjlo to 15% by weight of chromium oxide on a high purity, low sodium content gamma type alumina support,at'a temperature in the range from approximately 1200" F. to 1400 F., at a pressure in the range from 100 to 1000 p.s.i.g., at a weight hourly space velocityin the rangev from 0.5 to 2.0, whereby the alkylnaphthalene compounds are converted to naphthalene andgas, the additional step comprising, contacting said hydrocarbons with hot clay at a temperature of about 500 F.

17, The method of at least partially dealkylating an perature above approximately 1200 F. in the presence of hydrogen. ,l

References Cited in the file of this patent UNITED STATES PATENTS Coonradt et a1 Dec.' 18,,,1956

2,929,775 Aristoif et a1 Mar. 22,. 1960 

1. THE PROCESS OF PRODUCING NAPHTHALENE FROM A HYDROCARBON FEED STOCK CONTAINING ALKYLNAPHTHALENE COMPOUNDS WHICH PROCESS COMPRISES SUBJECTING THE FEED STOCK TO HYDRODEALKYLATING CONDITIONS IN THE PRESENCEOF HYDROGEN AND A CATALYST CONSISTING OF APPROXIMATELY 10 TO 15% BY WEIGHT OF CHROMIA ON A HIGH PURITY LOW SODIUM CON- 